I don't think there's a property for ScatterSky that lets you render a bottom half to it. If you were to use the Skybox class instead, that does let you specify a cubemap and get a complete surrounding sky without the whitespace, but at the expense of the cool features scattersky has like the day/night cycle.

What you could do is hide it, which will help in other ways too (nothing's more jarring than running into the edge of the world!)

The first is elevation. If you make the terrain itself higher on the Z Axis, the corners of the scattersky become a lot less apparent from the ground.

Also in this level there is a lot of terrain variation (default Outpost.mis). If there are hills blocking the whitespace, not only do you hide it but you also have a legit reason to prevent people from going to the edges and looking out into the abyss. Outpost is pretty big, only a small part of it is playable, the rest is just window dressing so it looks and feels like you're in the middle of something. Window dressing.

With intervening terrain, height, and designing the level in your favor, the last thing you can do to make it less obvious is adding fog to the level. I think even if you went to the edge of outpost you can barely see the black (or yellow I guess) just because it's fogged out and blends well.

There's also a waterPlane, which extends forever and does a lot to obscure it. Not always practical though.

Honestly if you ask me your best bet is to design maps in a way that there's always something obscuring the blank space, like steep cliffs or mountains in the horizon, and raising your level enough that players can't see the edges of the umbrella from the highest point. Alternatively, Skybox is always an option if you want to sacrifice some options.

1.Canvas clear color, it changes the black into whatever color you want, pick a color close to the sky so it becomes much elss visible. This method you should always use.

2.Use water plane if you can, it always fills up to the horizon.

3.Make mountains around the map to cover it up.

4.Make a really large low resolution terrain around your whole level, this will work similar to water plane.

5.Use skybox instead and sun object. You can also hack the scattersky to use skybox while setting the level to night time, picking a night skybox and changing night into day through sunlight colors etc.

6.Use fog to cover it up, whenever you have fog it will accumulate in the distance depending on settings, effectively covering up everything that could be going on there.This is by far my favorite method now. You can color the fog similar to the sky or similar to the terrain to simulate distant terrain.